1. Field of the Invention
The invention relates to a method and to apparatus for drying the ends of a bundle of hollow fibers for any membrane device in which the membrane is constituted by a bundle of hollow fibers that need to be kept moist and that need to be assembled to one another by gluing over a portion of their length.
2. Description of the Related Art
Such membrane devices are used in a variety of fields, and they are specifically adapted to their fields in particular by the selected chemical nature of their membranes. This category of membrane device includes, for example, certain types of water filter, reverse osmosis devices as used in particular for desalinating brine, and hemodialysers used for purifying the blood of people suffering from kidney failure, by dialysis and/or by filtering.
To illustrate the method of the invention and the apparatus for implementing it, the description below uses the example of hemodialysers, but it should be understood that this does not mean the invention is limited in any way to medical applications only.
In conventional manner, a hollow fiber hemodialyser includes a bundle of hollow fibers disposed in a tubular housing and held therein at both ends by gluing by means of a seal in which the fibers are embedded over a portion of their length, with the ends of the fibers being left open. The seals are installed so as to delimit a sealed chamber inside the housing. Endpieces are fitted to each of the ends of the housing whereby blood enters and leaves the housing by flowing along the inside of the fibers, with the housing further including two lateral ducts opening out into the sealed chamber whereby a dialysis liquid enters and leaves said chamber, which liquid therefore flows over the outsides of the fibers.
Whenever the fibers used need to be kept moist, and for whatever reasons, the manufacture of hemodialysers of this type suffers from a major technological difficulty which lies in the fabrication of the above-mentioned seals (the so-called "potting" operation). This applies, in particular, when the fibers are made of a material such as the copolymer of acrylonitrile and sodium methallyl sulfonate known under the trademark AN 69 which is made microporous by an appropriate method and which retains its structural characteristics only if it is kept moist. This also applies to fibers made of a material such as regenerated cellulose known under the trademark CUPROPHAN, which material is moistened in order to facilitate sterilization with ethylene oxide as applied to the hemodialyser at the end of manufacture.
The technological difficulty mentioned above is due to the fact that, at present, there exists no known glue capable of adhering to fibers having a water content above a certain value, which value is greatly exceeded with the fibers mentioned above.
To overcome this difficulty, French patent No. 72 29200 proposes a method of manufacturing a high pressure seal around a bundle of hollow fibers for a reverse osmosis device in which, to enable the sealforming glue to adhere to the fibers, that portion of the fibers which engages the glue is dried prior to gluing while the portion of the fibers that is to play an active role in the assembled device is kept moist. According to that patent, this result is achieved by coating the fibers with an elastomer material close to one end of the bundle of fibers to create a barrier between the end of the fibers that is to be engaged in the seal and the active portion of the fibers. The active portion of the fibers is immersed in an aqueous gelatin solution and because of the elastomer barrier, this solution is prevented from soaking the ends of the fibers by capillarity. The solution is cooled to solidify the gelatin. The ends of the fibers are dried and glue is then cast around them to form the seal. Finally, the gelatin surrounding the active portion of the fibers is removed, which gelatin has served to keep this portion of the fibers moist while the end of the bundle was being dried.
That method suffers from several drawbacks: it is heavy to implement; it is ill-suited to manufacturing membrane devices having substantially rectilinear bundles of fibers (e.g. the above-described hemodialysers); and it requires the fibers to be put into contact with various substances that constitute potential sources of pollution, which must be avoided absolutely with membrane devices for medical purposes.